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BQ25792: Ship Mode / ILIM_HIZ questions

AJ
Intellectual 570 points
Part Number: BQ25792

Hi Support Team,

According to the BQ25792 datasheet 

Ship Mode when SDRV_CTRL[1:0] = 10. The ship FET and the internal BATFET are both off. The I2C is still enabled. The charger can be woken up by setting SDRV_CTRL[1:0] back to 00, or pulling the QON pin low, or an adapter plug-in. This mode is only for the battery only condition

#1 What I don't understand is; if Ship FET is OFF, the battery is completely disconnected, how does the device remain powered up and accept I2C commands?

Input Current Limit

In the application circuit, V(ILIM_HIZ) = 2.2V, i.e. 5v x100k/(127k+100k) 
V(ILIM_HIZ) = 1V + 800mΩ × IINDPM, in which IINDPM  = 1.5A. However, the design parameters table 67 IINDPM register is set to 12Ch for 3A. 

#2 My understanding is that, the input current limit is set by lower setting of ILIM_HIZ pin and the IINDPM register. In this case, IINDPM would be 1.5A and not 3A.


Best,
AJ

  • 0
    TI__Genius 10240 points

    Hi Alex,

    We will get back to you after the July 4th holiday weekend.

  • 0 in reply to ezhao
    TI__Guru**** 166546 points

    Hi AJ,

    Regarding 1, the I2C engine is powered through BATP when the charger is in ship mode.

    Regarding 2, the input current limit setting per ILIM_HIZ pin is reported in ILIM from ICO register (REG19h bits 0:8) after POR.  If the EN_ILIM bit is high, the input current limit is the lower of IINDPM register or ILIM from ICO. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 570 points

    Hi Jeff,

    Thanks for the answer. 

    The reason I ask, is that the charge pump must have power to drive SRDV pin and trun ON the Ship FET. However, in the functional block diagram, the connection to battery is not shown. So I wanted to confirm. Now makes sense. 

    Though I am not sure how this feature is used if system is in ship mode and there is no power to MCU, i..e it's chick / egg situation you need power first in order to communicate with the charger over I2C... :-)

    Regarding #2, I believe you mean EN_EXTILIM.

    After POR, charger reads ILIM_HIZ voltage and sets ICO_ILIM bits accordingly. 

    if EN_EXTILIM =1 (default)
       ILIM = MIN ( IINDPM_8:0, ICO_ILIM_8:0)
    Else 
      ILIM = IINDPM_8:0

    Best,
    AJ

  • 0 in reply to AJ
    TI__Guru**** 166546 points

    AJ,

    You are correct in both responses!  

    Regards,

    Jeff